Hydropower is a clean, renewable and reliable energy source which converts kinetic energy from falling water into electricity, without consuming more water than is produced by nature.
The potential energy stored in a body of water held at a given height is converted to kinetic energy (movement energy) which is used to turn a turbine and create electricity.
Mechanical energy is derived by directing, harnessing, or channeling moving water. The amount of available energy in moving water is determined by its flow or fall.
In either instance, the water flows through a pipe, or penstock, then pushes against and turns blades in a turbine to spin a generator to produce electricity. In a run-of-the-river system, the force of the current applies the needed pressure, while in a storage system, water is accumulated in reservoirs created by dams, then released when the demand for electricity is high.
Hydro energy can be obtained by using many methods of capture. The most common method of using energy from water is a hydroelectric dam, where water coming down through an area causes turbines to rotate and the energy is captured to run a generator. Power can also be generated from the energy of tidal forces or wave power, which uses the energy created by waves.
A dam is built to trap water, usually in a valley where there is an existing lake. Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive generators.
The dam is much thicker at the bottom than at the top, because the pressure of the water increases with depth. Hydro-electric power stations can produce a great deal of power very cheaply.
This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations. A pumped-storage plant has two reservoirs- upper and lower.
Upper reservoir – Like a conventional hydropower plant, a dam creates a reservoir. The water in this reservoir flows through the hydropower plant to create electricity.
Lower reservoir – Water exiting the hydropower plant flows into a lower reservoir rather than re-entering the river and flowing downstream.
At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. Pumped-storage schemes currently provide the most commercially important means of large-scale grid energy storage and improve the daily capacity factor of the generation system
Run of the river
Run of the river hydroelectric stations are those with smaller reservoir capacities, thus making it impossible to store water
A tidal power plant makes use of the daily rise and fall of water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods. Less common types of hydro schemes use water’s kinetic energy or undammed sources such as undershot waterwheels.
Hydropower plants and environment
While offering ecological advantages from a global perspective, such as climate change mitigation, emergency management and reduction of ? ooding risk, the construction and operation of hydropower plants may cause some environmental impacts on the local and regional level. These include harm to ?sh populations, a loss of aquatic habitat, a signi? cant change in natural ? ow regimes and deterioration of the landscap
Damming rivers may destroy or disrupt wildlife and other natural resources. Some fish, like salmon, may be prevented from swimming upstream to spawn. Hydropower plants can also cause low dissolved oxygen levels in the water, which is harmful to river habitats.
A reservoir and operation of the dam can also change the natural water temperatures, chemistry, flow characteristics, and silt loads, all of which can lead to significant changes in the ecology (living organisms and the environment) and rocks and land forms of the river upstream and downstream. These changes may have negative impacts on native plants and animals in and next to the river, and in the deltas that form where rivers empty into the ocean. Reservoirs may cover important natural areas, agricultural land, and archeological sites, and cause the relocation of people.